Many measurement tasks involve the volumetric measurement of materials in liquid form. Such volumetric measurements may include measuring the amount of liquid taken from, for example, a lake, reservoir or other body of water which one wishes to test for environmental pollutants. In other applications, assembly line testing of samples may require reactants to be dispensed for use in a testing procedure. In similar fashion, manufacturing processes may require the input of measured amounts of reactants into a vessel in which a reaction, mixing, or other operation is being carried out.
Typically, relatively small measured quantities of liquids are removed from a larger quantity of liquid using a pipette. Pipettes generally come in two forms. Some pipettes comprise elongated tubes which have a volume which is at least somewhat larger than the volume of liquid which they are meant to remove. Such pipettes have an inlet tip at one end and an open port at the other end. Typically, the inlet tip of such a pipette is dipped into the source of the liquid which one wishes to measurably remove. By vacuum the liquid is drawn into the pipette up to a level marked by a graduation which is usually etched into or printed on the pipette. Generally, the volume between the inlet tip of the pipette and the graduation is the volume which the pipette is designed to sample or otherwise measurably remove. The open port at the other end of the pipette is then sealed in an airtight fashion. The pipette is then removed from the source of the liquid which one is sampling, and because of the relatively narrow diameter of the opening at the inlet tip of the pipette, the combined forces of air pressure acting at the interface of the atmosphere and the liquid being sampled and cohesive forces within the liquid being sampled act to prevent the liquid being sampled from flowing out the bottom of the pipette through the inlet tip of the pipette. Next, the pipette is placed over the vessel which is to receive the sampled liquid, the airtight seal at the port is opened, and the liquid in the pipette flows out the inlet tip of the pipette into the vessel which is to receive the liquid being sampled.
Airtight sealing of the open port of the pipette may be achieved simply by using a finger to tightly seal the open port. Alternatively, a pipette may be provided with a rubber bladder, which may be squeezed and then slowly released to allow the input of liquid up to the graduation. After this, the bladder may be depressed again to release the liquid being sampled.
While some pipettes simply comprise straight tubes, where large volumes of material are to be measurably removed, pipettes generally comprise a tube with a central area which comprises an enlarged bulbous portion. Both pipettes with and without a bulb may include either a single graduation if they are to be used to measure a single volume, or a plurality of graduations if they are to be used to measure a plurality of different volumes.
Typically, pipettes are used over and over again. Accordingly, if a pipette is being used for one material then another material, it is usually necessary to wash the pipette. Likewise, even if a pipette is being used only for a single material, if it is to lie unused for a period of time, material remaining on the pipette may react, dry out, or otherwise change, thus making it undesirable to leave a used pipette unwashed. Accordingly, pipettes are constantly being washed. It will be appreciated that pipettes must be washed both on the inside and the outside, although the challenge to obtain a well cleaned pipette is the thorough cleaning of the inside of the pipette.
Washing is complicated due to the narrow inner diameter of pipettes and the relatively inaccessible surfaces of bulbs on large volume pipettes. Accordingly, it is important that washing be carried out easily and thoroughly, as delay will often only make the washing operation more time-consuming and difficult to achieve with thoroughness.